In the related art, there is a known high-frequency treatment instrument in which a high-frequency current is applied so as to treat biological tissue, such as a mucous membrane (for example, see PTL 1).
In this high-frequency treatment instrument, a rod-shaped electrode portion is disposed by being inserted in a through-hole in an electrically insulating support member provided at the distal end of a sheath, so as to be advanceable/retractable in the axial direction. A wire that transmits a tensile force and that supplies the high-frequency current is connected to the proximal end of the rod-shaped electrode portion, and the rod-shaped electrode portion is advanced and retracted by operating an operating portion disposed at the proximal end of the sheath. In addition, an electrically insulating large-diameter portion is provided at the distal end of the rod-shaped electrode portion, and the large-diameter portion is provided with a through-hole that passes therethrough from the proximal end to the distal end.
Accordingly, in a state in which the rod-shaped electrode portion is moved to the extreme proximal end so that the large-diameter portion comes into close contact with the support member, liquid sent through the sheath can be discharged toward the front of the large-diameter portion via a gap between the through-hole in the support portion and the rod-shaped electrode portion and via the through-hole in the large-diameter portion.